"And if great reasoners are often maniacal, it is equally true that maniacs are often great reasoners. . . . If you argue with a madman, it is extremely provable that you will get the worse of it, for in many ways his mind moves all the quicker for not being delayed by the things that go with good judgement. He is not hampered by a sense of humour or by charity, or by the dumb certainties of experience. He is the more logical for losing certain sane affections. Indeed, the common phrase for insanity is in this respect a misleading one. The madman is not the man who has lost his reason. The madman is the man who has lost everything but his reason. The madman's explanation of a thing is always complete, and often in a purely rational sense satisfactory . . . . His mind moves in a perfect but narrow circle . . . . In the same way the insane explanation is quite as complete as the sane one, but it is not so large . . . . Now, speaking quite externally and empirically, we may say that the strongest and most unmistakable mark fo madness is this combination between a logical completion and a spiritual contraction . . . . He [the madman of experience] is in the clean and well-lit prison of one idea: he is sharpened to one painful point. . . ."
- G. K. Chesterton